Slot 2 includes the ports on the upper expansion module (if populated).

Slot 3 includes the ports on the lower expansion module (if populated).

Port number

Port number within the group.

The interface numbering convention is extended to support use with a Cisco Nexus 2000 Series Fabric Extender as follows:

switch(config)# interfaceethernet [chassis/]slot/port

Chassis ID is an optional entry to address the ports of a connected Fabric Extender. The chassis ID is configured on a physical Ethernet or EtherChannel interface on the switch to identify the Fabric Extender discovered via the interface. The chassis ID ranges from 100 to 199.

About the Unidirectional Link Detection Parameter

UDLD Overview

The Cisco-proprietary Unidirectional Link Detection (UDLD) protocol allows ports that are connected through fiber optics or copper (for example, Category 5 cabling) Ethernet cables to monitor the physical configuration of the cables and detect when a unidirectional link exists. When the switch detects a unidirectional link, UDLD shuts down the affected LAN port and alerts the user. Unidirectional links can cause a variety of problems, including spanning tree topology loops.

UDLD is a Layer 2 protocol that works with the Layer 1 protocols to determine the physical status of a link. At Layer 1, autonegotiation takes care of physical signaling and fault detection. UDLD performs tasks that autonegotiation cannot perform, such as detecting the identities of neighbors and shutting down misconnected LAN ports. When you enable both autonegotiation and UDLD, Layer 1 and Layer 2 detections work together to prevent physical and logical unidirectional connections and the malfunctioning of other protocols.

A unidirectional link occurs whenever traffic transmitted by the local device over a link is received by the neighbor but traffic transmitted from the neighbor is not received by the local device. If one of the fiber strands in a pair is disconnected, as long as autonegotiation is active, the link does not stay up. In this case, the logical link is undetermined, and UDLD does not take any action. If both fibers are working normally at Layer 1, then UDLD at Layer 2 determines whether those fibers are connected correctly and whether traffic is flowing bidirectionally between the correct neighbors. This check cannot be performed by autonegotiation, because autonegotiation operates at Layer 1.

A Cisco Nexus 5000 Series switch periodically transmits UDLD frames to neighbor devices on LAN ports with UDLD enabled. If the frames are echoed back within a specific time frame and they lack a specific acknowledgment (echo), the link is flagged as unidirectional and the LAN port is shut down. Devices on both ends of the link must support UDLD in order for the protocol to successfully identify and disable unidirectional links.

Note

By default, UDLD is locally disabled on copper LAN ports to avoid sending unnecessary control traffic on this type of media.

The following figure shows an example of a unidirectional link condition. Device B successfully receives traffic from Device A on the port. However, Device A does not receive traffic from Device B on the same port. UDLD detects the problem and disables the port.

Figure 1. Unidirectional Link

Default UDLD Configuration

The following table shows the default UDLD configuration.

Table 1 UDLD Default Configuration

Feature

Default Value

UDLD global enable state

Globally disabled

UDLD aggressive mode

Disabled

UDLD per-port enable state for fiber-optic media

Enabled on all Ethernet fiber-optic LAN ports

UDLD per-port enable state for twisted-pair (copper) media

Disabled on all Ethernet 10/100 and 1000BASE-TX LAN ports

UDLD Aggressive and Nonaggressive Modes

UDLD aggressive mode is disabled by default. You can configure UDLD aggressive mode only on point-to-point links between network devices that support UDLD aggressive mode. If UDLD aggressive mode is enabled, when a port on a bidirectional link that has a UDLD neighbor relationship established stops receiving UDLD frames, UDLD tries to reestablish the connection with the neighbor. After eight failed retries, the port is disabled.

To prevent spanning tree loops, nonaggressive UDLD with the default interval of 15 seconds is fast enough to shut down a unidirectional link before a blocking port transitions to the forwarding state (with default spanning tree parameters).

When you enable the UDLD aggressive mode, the following occurs:

One side of a link has a port stuck (both transmission and receive)

One side of a link remains up while the other side of the link is down

In these cases, the UDLD aggressive mode disables one of the ports on the link, which prevents traffic from being discarded.

About Interface Speed

A Cisco Nexus 5000 Series switch has a number of fixed 10-Gigabit ports, each equipped with SFP+ interface adapters. The Cisco Nexus 5010 switch has 20 fixed ports, the first 8 of which are switchable 1-Gigabit and 10-Gigabit ports. The Cisco Nexus 5020 switch has 40 fixed ports, the first 16 of which are switchable 1-Gigabit and 10-Gigabit ports.

CDP runs on all media that support Subnetwork Access Protocol (SNAP). Because CDP runs over the data-link layer only, two systems that support different network-layer protocols can learn about each other.

Each CDP-configured device sends periodic messages to a multicast address, advertising at least one address at which it can receive SNMP messages. The advertisements also contain time-to-live, or holdtime information, which is the length of time a receiving device holds CDP information before discarding it. Each device also listens to the messages sent by other devices to learn about neighboring devices.

About the Error-Disabled State

An interface is in the error-disabled (err-disabled) state when the inteface is enabled administratively (using the no shutdown command) but disabled at runtime by any process. For example, if UDLD detects a unidirectional link, the interface is shut down at runtime. However, because the interface is administratively enabled, the interface status displays as err-disabled. Once an interface goes into the err-disabled state, you must manually reenable it or you can configure an automatic timeout recovery value. The err-disabled detection is enabled by default for all causes. The automatic recovery is not configured by default.

When an interface is in the err-disabled state, use the errdisable detect cause command to find information about the error.

You can configure the automatic err-disabled recovery timeout for a particular err-disabled cause by changing the time variable.

The errdisable recovery cause command provides automatic recovery after 300 seconds. To change the recovery period, use the errdisable recovery interval command to specify the timeout period. You can specify 30 to 65535 seconds.

If you do not enable the err-disabled recovery for the cause, the interface stays in the err-disabled state until you enter the shutdown and no shutdown commands. If the recovery is enabled for a cause, the interface is brought out of the err-disabled state and allowed to retry operation once all the causes have timed out. Use the show interface status err-disabled command to display the reason behind the error.

About the Debounce Timer Parameters

The port debounce time is the amount of time that an interface waits to notify the supervisor of a link going down. During this time, the interface waits to see if the link comes back up. The wait period is a time when traffic is stopped.

You can enable the debounce timer for each interface and specify the delay time in milliseconds.

Caution

When you enable the port debounce timer the link up and link down detections are delayed, resulting in a loss of traffic during the debounce period. This situation might affect the convergence and reconvergence of some protocols.

About MTU Configuration

The Cisco Nexus 5000 Series switch is a Layer 2 device. This means it does not fragment frames. As a result, the switch cannot have two ports in the same Layer 2 domain with different maximum transmission units (MTUs). A per-physical Ethernet interface MTU is not supported. Instead, the MTU is set according to the QoS classes. You modify the MTU by setting Class and Policy maps.

Note

When you show the interface settings, a default MTU of 1500 is displayed for physical Ethernet interfaces and a receive data field size of 2112 is displayed for Fibre Channel interfaces.

Configuring Ethernet Interfaces

Configuring the UDLD Mode

You can configure normal or aggressive unidirectional link detection (UDLD) modes for Ethernet interfaces on devices configured to run UDLD. Before you can enable a UDLD mode for an interface, you must make sure that UDLD is already enabled on the device that includes the interface. UDLD must also be enabled on the other linked interface and its device.

To use the normal UDLD mode, you must configure one of the ports for normal mode and configure the other port for the normal or aggressive mode. To use the aggressive UDLD mode, you must configure both ports for the aggressive mode.

Note

Before you begin, UDLD must be enabled for the other linked port and its device.

To configure the UDLD mode, perform this task:

SUMMARY STEPS

1.switch# configure terminal

2.switch(config)# feature udld

3.switch(config)# no feature udld

4.switch(config)# show udld global

5.switch(config)# interfacetypeslot/port

6.switch(config-if)# udld {enable | disable | aggressive}

7.switch(config-if)# show udldinterface

DETAILED STEPS

Command or Action

Purpose

Step 1

switch# configure terminal

Enters configuration mode.

Step 2

switch(config)# feature udld

Enables UDLD for the device.

Step 3

switch(config)# no feature udld

Disables UDLD for the device.

Step 4

switch(config)# show udld global

Displays the UDLD status for the device.

Step 5

switch(config)# interfacetypeslot/port

Specifies an interface to configure, and enters interface configuration mode.

This example shows how to enable the normal UDLD mode for an Ethernet port:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# udld enable

This example shows how to enable the aggressive UDLD mode for an Ethernet port:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# udld aggressive

This example shows how to disable UDLD for an Ethernet port:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# udld disable

This example shows how to disable UDLD for the switch:

switch# configure terminal

switch(config)# no feature udld

Configuring Interface Speed

The first 8 ports of a Cisco Nexus 5010 switch and the first 16 ports of a Cisco Nexus 5020 switch are switchable 1-Gigabit and 10-Gigabit ports. The default interface speed is 10-Gigabit. To configure these ports for 1-Gigabit Ethernet, insert a 1-Gigabit Ethernet SFP transceiver into the applicable port and then set its speed with the speed command.

To configure a 1-Gigabit Ethernet port, perform this task:

SUMMARY STEPS

1.switch# configure terminal

2.switch(config)# interfacetypeslot/port

3.switch(config-if)# speedspeed

DETAILED STEPS

Command or Action

Purpose

Step 1

switch# configure terminal

Enters configuration mode.

Step 2

switch(config)# interfacetypeslot/port

Enters interface configuration mode for the specified interface. This interface must have a 1-Gigabit Ethernet SFP transceiver inserted into it.

Step 3

switch(config-if)# speedspeed

Sets the speed on the interface.

The following example shows how to set the speed for a 1-Gigabit Ethernet port:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# speed 1000

This command can only be applied to a physical Ethernet interface.

Note

If the interface and transceiver speed is mismatched, the SFP validation failed message is displayed when you enter the show interface ethernetslot/port command. For example, if you insert a 1-Gigabit SFP transceiver into a port without configuring the speed 1000 command, you will get this error. By default, all ports are 10 Gigabits.

Configuring the Cisco Discovery Protocol

Configuring the CDP Characteristics

You can configure the frequency of Cisco Discovery Protocol (CDP) updates, the amount of time to hold the information before discarding it, and whether or not to send Version-2 advertisements.

Configures the format of the CDP device ID. The default is the system name, which can be expressed as a fully qualified domain name.

Use the no form of the command to return to its default setting.

Step 4

switch(config)# [no] cdp holdtimeseconds

(Optional)

Specifies the amount of time a receiving device should hold the information sent by your device before discarding it. The range is 10 to 255 seconds; the default is 180 seconds.

Use the no form of the command to return to its default setting.

Step 5

switch(config)# [no] cdp timerseconds

(Optional)

Sets the transmission frequency of CDP updates in seconds. The range is 5 to 254; the default is 60 seconds.

Use the no form of the command to return to its default setting.

This example shows how to configure CDP characteristics:

switch# configure terminal

switch(config)# cdp timer 50

switch(config)# cdp holdtime 120

switch(config)# cdp advertise v2

Enabling or Disabling CDP

You can enable or disable CDP for Ethernet interfaces. This protocol works only when you have it enabled on both interfaces on the same link.

To enable or disable CDP for an interface, perform this task:

SUMMARY STEPS

1.switch# configure terminal

2.switch(config)# interfacetypeslot/port

3.switch(config-if)# cdp enable

4.switch(config-if)# no cdp enable

DETAILED STEPS

Command or Action

Purpose

Step 1

switch# configure terminal

Enters configuration mode.

Step 2

switch(config)# interfacetypeslot/port

Enters interface configuration mode for the specified interface.

Step 3

switch(config-if)# cdp enable

Enables CDP for the interface.

To work correctly, this parameter must be enabled for both interfaces on the same link.

Step 4

switch(config-if)# no cdp enable

Disables CDP for the interface.

The following example shows how to enable CDP for an Ethernet port:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# cdp enable

This command can only be applied to a physical Ethernet interface.

Enabling the Error-Disabled Detection

You can enable error-disable (err-disabled) detection in an application. As a result, when a cause is detected on an interface, the interface is placed in an err-disabled state, which is an operational state that is similar to the link-down state.

SUMMARY STEPS

1. config t

2.errdisable detect cause {all | link-flap | loopback}

3.shutdown

4.no shutdown

5.show interface status err-disabled

6.copy running-config startup-config

DETAILED STEPS

Command or Action

Purpose

Step 1

config t

Example:

switch# config t
switch(config)#

Enters configuration mode.

Step 2

errdisable detect cause {all | link-flap | loopback}

Example:

switch(config)# errdisable detect cause all
switch(config)#

Specifies a condition under which to place the interface in an err-disabled state. The default is enabled.

Step 3

shutdown

Example:

switch(config)# shutdown
switch(config)#

Brings the interface down administratively. To manually recover the interface from the err-disabled state, enter this command first.

Step 4

no shutdown

Example:

switch(config)# no shutdown
switch(config)#

Brings the interface up administratively and enables the interface to recover manually from the err-disabled state.

Step 5

show interface status err-disabled

Example:

switch(config)# show interface status err-disabled

Displays information about err-disabled interfaces.

Step 6

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

This example shows how to enable the err-disabled detection in all cases:

switch(config)#errdisable detect cause all
switch(config)#

Enabling the Error-Disabled Recovery

You can specify the application to bring the interface out of the error-disabled (err-disabled) state and retry coming up. It retries after 300 seconds, unless you configure the recovery timer (see the errdisable recovery interval command).

Specifies a condition under which the interface automatically recovers from the err-disabled state, and the device retries bringing the interface up. The device waits 300 seconds to retry. The default is disabled.

Step 3

show interface status err-disabled

Example:

switch(config)#show interface status err-disabled

Displays information about err-disabled interfaces.

Step 4

copy running-config startup-config

Example:

switch(config)#copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

This example shows how to enable err-disabled recovery under all conditions:

switch(config)#errdisable recovery cause all
switch(config)#

Configuring the Error-Disabled Recovery Interval

You can use this procedure to configure the err-disabled recovery timer value. The range is from 30 to 65535 seconds. The default is 300 seconds.

SUMMARY STEPS

1.config t

2.errdisable recovery intervalinterval

3.show interface status err-disabled

4.copy running-config startup-config

DETAILED STEPS

Command or Action

Purpose

Step 1

config t

Example:

switch#config t
switch(config)#

Enters configuration mode.

Step 2

errdisable recovery intervalinterval

Example:

switch(config)#errdisable recovery interval 32
switch(config-if)#

Specifies the interval for the interface to recover from the err-disabled state. The range is from 30 to 65535 seconds. The default is 300 seconds.

Step 3

show interface status err-disabled

Example:

switch(config)#show interface status err-disabled

Displays information about err-disabled interfaces.

Step 4

copy running-config startup-config

Example:

switch(config)#copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

This example shows how to enable err-disabled recovery under all conditions:

switch(config)#errdisable recovery cause all
switch(config)#

Configuring the Debounce Timer

You can enable the debounce timer for Ethernet ports by specifying a debounce time (in milliseconds) or disable the timer by specifying a debounce time of 0.

You can show the debounce times for all of the Ethernet ports by using the show interface debounce command.

To enable or disable the debounce timer, perform this task:

SUMMARY STEPS

1.switch# configure terminal

2.switch(config)# interfacetypeslot/port

3.switch(config-if)# link debounce timemilliseconds

DETAILED STEPS

Command or Action

Purpose

Step 1

switch# configure terminal

Enters configuration mode.

Step 2

switch(config)# interfacetypeslot/port

Enters interface configuration mode for the specified interface.

Step 3

switch(config-if)# link debounce timemilliseconds

Enables the debounce timer for the amount of time (1 to 5000 milliseconds) specified.

Disables the debounce timer if you specify 0 milliseconds.

This example shows how to enable the debounce timer and set the debounce time to 1000 milliseconds for an Ethernet interface:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# link debounce time 1000

This example shows how to disable the debounce timer for an Ethernet interface:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# link debounce time 0

This command can only be applied to a physical Ethernet interface.

Configuring the Description Parameter

To provide textual interface descriptions for the Ethernet ports, perform this task:

SUMMARY STEPS

1.switch# configure terminal

2.switch(config)# interfacetypeslot/port

3.switch(config-if)# descriptiontest

DETAILED STEPS

Command or Action

Purpose

Step 1

switch# configure terminal

Enters configuration mode.

Step 2

switch(config)# interfacetypeslot/port

Enters interface configuration mode for the specified interface.

Step 3

switch(config-if)# descriptiontest

Specifies the description for the interface.

This example shows how to set the interface description to "Server 3 Interface."

switch# configure terminal

switch(config)# interface ethernet 1/3

switch(config-if)# description Server 3 Interface

Disabling and Restarting Ethernet Interfaces

You can shut down and restart an Ethernet interface. This action disables all of the interface functions and marks the interface as being down on all monitoring displays.

To disable an interface, perform this task:

SUMMARY STEPS

1.switch# configure terminal

2.switch(config)# interfacetypeslot/port

3.switch(config-if)# shutdown

4.switch(config-if)# no shutdown

DETAILED STEPS

Command or Action

Purpose

Step 1

switch# configure terminal

Enters configuration mode.

Step 2

switch(config)# interfacetypeslot/port

Enters interface configuration mode for the specified interface.

Step 3

switch(config-if)# shutdown

Disables the interface.

Step 4

switch(config-if)# no shutdown

Restarts the interface.

The following example shows how to disable an Ethernet port:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# shutdown

The following example shows how to restart an Ethernet interface:

switch# configure terminal

switch(config)# interface ethernet 1/4

switch(config-if)# no shutdown

Displaying Interface Information

To view configuration information about the defined interfaces, perform one of these tasks:

Command

Purpose

switch# show interfacetypeslot/port

Displays the detailed configuration of the specified interface.

switch# show interfacetypeslot/portcapabilities

Displays detailed information about the capabilities of the specified interface. This option is only available for physical interfaces

switch# show interfacetypeslot/porttransceiver

Displays detailed information about the transceiver connected to the specified interface. This option is only available for physical interfaces.

switch# show interface brief

Displays the status of all interfaces.

switch# show interface debounce

Displays the debounce status of all interfaces.

switch# show interface flowcontrol

Displays the detailed listing of the flow control settings on all interfaces.

The show interface command is invoked from EXEC mode and displays the interface configurations. Without any arguments, this command displays the information for all the configured interfaces in the switch.

The following example shows how to display the physical Ethernet interface:

From Cisco NX-OS Release 4.0(1a)N1(1), the default value of the device ID field for CDP advertisement has been changed from the chassis serial number to the hostname and serial number, as in the example above.

Default Physical Ethernet Settings

The following table lists the default settings for all physical Ethernet interfaces: